Tool retraction receiving element and adapter for positioning the same

ABSTRACT

The invention relates to a tool retraction receiving element comprising a receiving section ( 3 ) for retracting a tool ( 15 ) and a clamping section ( 9 ) for clamping said tool retraction receiving element ( 1 ) in a tool receiving carrier. Said tool retraction receiving element is characterised in that the receiving section ( 3 ) for the tool ( 15 ) and the clamping section ( 9 ) of the tool retraction receiving element ( 1 ) overlap in the longitudinal direction. The invention also relates to an adapter for positioning one such tool retraction receiving element.

The invention relates to a tool retraction receiving element with a receiving section for retracting a tool and a clamping section for clamping the tool retraction receiving element in a tool receiving carrier. The invention also relates to an adapter for positioning of the tool retraction receiving element.

In conventional shrink-fit tool holders the holding section for shrinking fitting the tool is configured on one end of the shrink-fit tool holder. The clamping section for clamping the shrink-fit tool holder in a tool holder support is configured in the longitudinal direction spaced away from the holding section for the tool on the opposite end of the tool holder. When shrink-fitted tools are being used on a machine tool, for example a milling machine, lathe, or drilling machine, the surface of the workpiece, which in particular has been machined by cutting, often does not have the desired quality.

The object of the invention is to make available a shrink-fit tool holder of the initially described type and the pertinent adapter for accommodating a shrink-fit tool holder by which the disadvantages of the prior art can be overcome, especially by which better surface qualities of the machined workpieces can be achieved.

In a shrink-fit tool holder with a holding section for shrink-fitting of a tool and a clamping section for clamping the shrink-fit tool holder in a tool holder support the object is achieved in that the holding section for the tool and the clamping section of the shrink-fit tool holder overlap in the longitudinal direction. By superposition of the holding section for the tool with the clamping section in the axial direction, short, compact shrink-fit tool holders can be formed which have very high stiffness, especially in the radial direction. This in turn leads to better surface quality of the machined workpieces. Moreover the service life of the tools can be increased by the short structural length of the shrink-fit tool holder.

One preferred embodiment of the shrink-fit tool holder is characterized in that the overlapping is more than 50% of the total length of the shrink-fit tool holder; for many applications it is sufficient if the overlapping is more than 30%. In this way deflection of the shrink-fit tool holder in the radial direction is avoided in operation.

Another preferred embodiment of the shrink-fit tool holder is characterized in that the overlapping extends essentially over the entire length of the clamping section for clamping the shrink-fit tool holder in a tool holder support. At least one partial section with an extension which is approximately 5% of the total length of the shrink-fit tool holder can be configured without overlapping.

Another preferred embodiment of the shrink-fit tool holder is characterized in that the holding section for shrinking fitting of the tool is formed by a through hole which extends over the entire length of the shrink-fit tool holder. The through hole preferably has a circular cross section, but can also have a polygonal cross section.

Another preferred embodiment of the shrink-fit tool holder is characterized in that the through hole on its end opposite the clamping section has a centering section with a widened inside diameter. The centering section is used to hold and center, before shrink fitting, one end of the tool which is to be shrink-fitted.

Another preferred embodiment of the shrink-fit tool holder is characterized in that following the clamping section, a circumferential groove is formed which has an especially rectangular cross section. The circumferential groove interacts with a cam which is configured on a clamping nut and is used to release the tool holder after machining.

Another preferred embodiment of the shrink-fit tool holder is characterized in that on the end of the shrink-fit tool holder, opposite the clamping section, following the circumferential groove a conical section is formed which widens toward the circumferential groove. The conical section facilitates placement of a tensioning nut.

Another preferred embodiment of the shrink-fit tool holder is characterized in that the clamping section has the shape of a cone. The dimensions of the cone are preferably standardized, for example according to DIN 6499.

Another preferred embodiment of the shrink-fit tool holder is characterized in that the clamping section has the shape of a circular cylinder. The configuration of the clamping section is matched to the shape of the tool holder support.

An adapter for use with the previously described shrink-fit tool holder is characterized by a depression with dimensions which are matched to the end of the clamping section of the shrink-fit tool holder. The depression can be configured as a conical or cylindrical depression and ensures that almost the entire outer circumferential surface of the shrink-fit tool holder is accessible from the outside in order to deliver heat to the shrink-fit tool holder. The depth of the depression is chosen such that tilting of the tool holder in place is reliably prevented. With inductive heating and an electrically conductive, especially metallic adapter the vertical dimension of the depression is comparatively small, for example 1 to 5, especially approximately 2 mm.

One preferred embodiment of the adapter is characterized in that the adapter tapers toward the shrink-fit tool holder. Tapering simplifies the placement of the heating element on the adapter.

Another preferred embodiment of the adapter is characterized in that the adapter is configured as at least two parts and comprises a base adapter and an adapter insert on which the depression and/or the tapering is/are configured. This facilitates use of the base adapter for shrink-fit tool holders of different sizes. The different shrink-fit tool holders together with the pertinent adapter inserts can be used with one and the same base adapter. The base adapter in turn is matched to the heating device which is to be used.

Another preferred embodiment of the adapter is characterized by a central threaded hole in which a threaded bolt is held with a turning capacity, with a free end which forms a stop for the tool when the shrink-fit tool holder is positioned on the adapter. By turning the threaded bolt the shrink-fitting depth of the tool can be continuously adjusted.

Other advantages, features and details of the invention follow from the description below in which one embodiment will be described in detail with reference to the drawings. The features mentioned in the claims and the specification can be essential for the invention each individually or in any combination.

FIG. 1 shows a shrink-fit tool holder as claimed in the invention in a longitudinal section;

FIG. 2 shows the shrink-fit tool holder from FIG. 1 before the tool is shrink-fitted;

FIG. 3 shows the shrink-fit tool holder from FIG. 1 when the tool is being centered;

FIG. 4 shows the shrink-fit tool holder from FIG. 1 with the tool shrink-fitted;

FIG. 5 shows an adapter insert for positioning of the shrink-fit tool holder shown in FIG. 1 in a longitudinal section;

FIG. 6 shows a base adapter for use with the adapter insert shown in FIG. 5 in a longitudinal section;

FIG. 7 shows an enlargement of detail VII from FIG. 6;

FIG. 8 shows the base adapter from FIG. 6 with the adapter insert in place;

FIG. 9 shows the adapter from FIG. 8 with the shrink-fit tool holder in place;

FIG. 10 shows a second embodiment of a shrink-fit tool holder as claimed in the invention in a longitudinal section;

FIG. 11 shows the second embodiment of FIG. 10 in a perspective view;

FIG. 12 shows a third embodiment of a shrink-fit tool holder as claimed in the invention in a longitudinal section;

FIG. 13 shows the third embodiment of FIG. 12 in a perspective view; and

FIG. 14 shows a second embodiment of an adapter as claimed in the invention with the shrink-fit tool holder inserted, in a longitudinal section.

FIG. 1 shows a shrink-fit tool holder 1 which has a through hole 3 for holding the tool shaft 16 of a tool 15 (see FIGS. 2 to 4). The through hole 3 has a section 5 with a constant inside diameter. On one end the section 5 undergoes transition into a centering section 6 with a slightly widened inside diameter. On the other end the section 5 undergoes transition into a section 7 with a likewise slightly widened inside diameter.

The shrink-fit tool holder 1 is configured rotationally symmetrical and on its outer circumference has a conical clamping section 9 which tapers toward the end. The widening end of the clamping section 9 is adjoined by a circumferential groove 10 which is used to hold the cam of a clamping screw (not shown). The circumferential groove 10 in the axial direction is followed by a conical section 12 which tapers away from the circumferential groove 10. The conical section 12 is used to ensure simple positioning or sliding over of the clamping nut with the cam. For this purpose the largest outside diameter of the conical section 12 is larger than the pertinent inside diameter of the clamping nut with the cam.

FIG. 2 shows the tool 15, for example a drill, shortly before shrink-fitting into the shrink-fit tool holder. In FIG. 3 the free end of the tool shaft 16 for its centering is inserted into the centering section 6 of the shrink-fit tool holder 1. In FIG. 4 the shaft 16 of the tool 15 is shrink-fitted into the through hole 3.

FIG. 5 shows an adapter insert 20 in a longitudinal section. The adapter insert 20 is configured rotationally symmetrical and comprises a depression 22 which is used to hold the free end of the clamping section of the shrink-fit tool holder which is shown in FIG. 1. The depression 22 can be made as a cylindrical depression. In FIG. 5 the depression 22 is made slightly conical to facilitate the placement of the shrink-fit tool holder.

The adapter insert 20 is equipped with a through hole 23. The hole 23 comprises one hole section 24 and one hole section 25, the hole section 24 having a larger inside diameter than the hole section 25; in the hole section 25 the hole 23 is penetrated by a through hole 26 which extends perpendicular to the through hole 23. The hole 26 is used to hold a pretensioned ball which is used in turn to fix the adapter insert 10 in a base adapter (see FIG. 6). The through hole 23 extends centrally through the adapter insert 20 and at the same time forms the longitudinal axis of the rotationally symmetrical component.

On its outer circumference the adapter insert 20 comprises four sections 29, 30, 31, and 32. The section 29 is located in the area of the depression 22 and is made slightly conical, the section 29 tapering toward its free end. The section 30 follows the conical section 29 and has a constant outside diameter. The section 31 adjoins the section 30 and widens from the section 30 in a conical shape. The section 32 follows the section 31 and has a somewhat smaller outside diameter than the section 30.

FIG. 6 shows the base adapter 35 in a longitudinal section which is likewise configured rotationally symmetrical. The base adapter 35 is equipped with a central holding hole 37 with an inside diameter which is matched to the outside diameter of the section 32 of the adapter insert 20. In this way insertion of the adapter insert 20 with the section 32 into the holding hole 37 of the base adapter 35 is facilitated.

A circumferential groove with a triangular cross section is formed in the holding hole 37. In the enlarged sectional view in FIG. 7 it is shown that the groove flanks of the triangular groove 38 are configured at an angle 39 to one another.

As is shown in FIG. 6, the holding hole 37 is part of a central through hole 40 which forms the longitudinal axis or axis of rotation of the base adapter 35. The through hole 40 comprises three additional sections 41, 42, and 43 with different inside diameters, proceeding from the holding hole 37. The hole section 41 has the smallest and the hole section 43 has the largest inside diameter. In addition an inside thread is formed in the hole section 41. On the outside the base adapter 35 has a section 44 with a widened outside diameter.

FIG. 8 shows the base adapter 35 from FIG. 6 with the adapter insert 20 from FIG. 5 in place. As is to be seen, the section 32 of the adapter insert 20 is held in the holding hole 37 of the base adapter 35. A threaded bolt 50 is screwed into the section 41 with the inside thread of the base adapter 35, of which bolt one free end projects into the section 42 of the through hole 40, and of which the other free end 51 projects into the hole section 24 of the adapter insert 20. Moreover, in the through hole 26 of the adapter insert 20 a ball 22 is pretensioned using a spring 53. The ball 52 is partially pressed out of the through hole 26 by the spring 53. The part of the ball 52 projecting out of the through hole 26 when the adapter insert 20 is in place is held in the groove 38 of the base adapter 35. In this way unwanted loosening of the adapter insert 20 from the base adapter 35 is prevented.

FIG. 9 shows how the shrink-fit tool holder 1 shown in FIG. 1 is positioned with the free end of the clamping section 9 on the depression 22 of the adapter insert 20. The section 43 of the through hole 40 is used to connect the base adapter 35 to a heater (not shown).

By heating the shrink-fit tool holder as claimed in the invention and by the resulting widening of the through hole 3 the tool shaft 16 of a tool 15 can be reversibly connected securely to the shrink-fit tool holder 1. The through hole 3 of the shrink-fit tool holder 1 relative to the cylindrical tool shaft 16 is configured smaller by at least approximately 0.01 mm, especially by at least approximately 0.02 mm, than the clamping diameter of the cutting tool 15. The overlap of the inside diameter of the through hole 3 and the outside diameter of the tool shaft 16 is influenced among other factors by the material used. As a result of the change in the volume of solids, which is proportional to the temperature when heated, the inside diameter of the through hole 3 of the shrink-fit tool holder 1 is enlarged. The widening by heating is carried out in the elastic range of the material. Thus the clamping process can be repeated as often as desired, that is, the process is reversible.

Heating when the tool shaft is being shrink-fitted into the through hole of the shrink-fit tool holder takes place in the temperature range from +100 to +380° C., especially +250 to +330°C. In the heated state of the shrink-fit tool holder 1 the optionally supercooled tool shaft 16 can be inserted into the through hole 3. Upon subsequent cooling of the shrink-fit tool holder 1 with the tool shaft 16 inserted to temperatures in the range from −20 to +110° C., the shrink-fit tool holder 1 tries to reach its initial state again. In the process a clamping pressure is produced on the cylindrical tool shaft 16 in the radial direction by cooling of the shrink-fit tool holder 1. The level of the clamping pressure is determined primarily by the overlap of the outside diameter of the tool shaft 16 with the inside diameter of the through hole 3 of the shrink-fit tool holder 1. Little overlapping results in a low clamping pressure. Extensive overlapping results in a high clamping pressure. The clamping process is reversible and can be repeated any number of times as long as the deformation takes place in the elastic area of the material used.

In the conventional processes the shrinkage area lies outside the clamping insert. This has the disadvantage that for each cutting tool clamping shaft diameter a correspondingly complex and expensive tool holder is needed. The long structural shape moreover has the disadvantage that the radial load of the machining spindle rises significantly; this then leads to a loss of stiffness and radial deflection of the machining spindle.

The shrink-clamping system as claimed in the invention does not require expensive, special tool holders, but can be installed in conventional universal draw-in collet chucks or machining spindles with collet chuck holders. By superposition of the shrinkage area with the clamping area the shortest cutting tool chucking mechanisms can be accomplished. One major advantage is the maximum radial stiffness of the machining tools. This in turn results in extremely high surface qualities of the machined workpieces.

The shrinking-clamping process as claimed in the invention takes place directly in the clamping cone. In this way extremely short clamping of the cutting tools is possible. The clamp insert hole which is also designated as the through hole 1 is superimposed by the clamping cone which is also designated as the clamping section 9. The shrink-fit clamping insert which is also designated as the shrink-fit tool holder 1 is very inexpensive to produce and can be inserted into any commercial standard collet holder. The shrink-fit tool holder 1 as claimed in the invention compared to conventional clamping techniques makes possible two to four times higher torque transmission with simultaneously higher radial stiffness.

The shrinking-clamping system as claimed in the invention enables short shrinking-in and shrinking-out times. A tool can be changed in seconds by inductive heating of the shrink-fit tool holder with high energy density. In this way true running accuracies of the cutting tools of less than 3 μm can be implemented with maximum clamping force and radial stiffness.

The shrink-fitting of a tool shaft into a shrink-fit holder using an adapter as claimed in the invention is described in what follows. First, the base adapter 35 must be connected to a suitable adapter insert 20 which is dependent on the shape and dimensions of the shrink-fit tool holder 1. Then the adapter which has been preassembled in this way is inserted into the base holder of a shrinking device (not shown). Then the shrink-fit tool holder 1 is slipped onto the adapter insert 20. Then an induction coil (not shown) is centered and fixed over the shrink-fit tool holder 1. After that the tool shaft 16 is inserted into the centering section 6 of the through hole 3. Then the shrinkage device is activated.

The through hole 3 of the shrink-fit tool holder 1 is enlarged by the change in volume which is proportional to temperature. As soon as widening of the through hole 3 of the shrink-fit tool holder 1 is greater than the outside diameter of the tool shaft 16, the tool 15 by its own weight falls into the through hole 3. The free end 51 of the threaded spindle 50 forms a stop for the free end of the tool shaft 16. Then the heat source can be turned off. Due to the cooling which now follows the shrink-fit tool holder 1 tries to attain its original shape; this however is prevented by the tool shaft 16. The resulting stress provides for the tool shaft 16 to be held positively and nonpositively in the shrink-fit tool holder 1.

To accelerate the cooling process, the shrink-fit tool holder 1 with the tool shaft 16 located in it can be cooled in a cooling station (not shown).

FIG. 10 shows a second embodiment of a shrink-fit tool holder 101 as claimed in the invention in a longitudinal section and FIG. 11 shows the pertinent perspective view. The holding section 103 is formed by an opening which extends in the longitudinal direction of the shrink-fit tool holder, in this embodiment by a through hole which extends over the entire length. The end of the opening which is the left end in FIG. 10 and which holds the tool is radially widened, in particular a radius 161 is molded on this end, as especially the enlargement of the corresponding extract of FIG. 10 shows. The radius 161 is generally less than half the diameter of the holding section 103, especially less than 20% of it, and preferably in the range of one mm or less. In this way the tool can be easily and precisely inserted into the shrink-fit tool holder 101 without tilting.

On its end facing the clamping section 109 the shrink-fit tool holder 101 has an opening which extends in the longitudinal direction of the shrink-fit tool holder and which forms another section 107, with a diameter which is greater than that of the holding section 103. The opening as in the embodiment shown can be a section of a through hole, but could also be made as a blind hole. The opening is preferably cylindrical in the longitudinal direction, especially circular-cylindrical.

Due to the greater diameter the wall thickness of the clamping section 109 is reduced in this further section 107, for example down to a few mm or only 1 mm on the free end. This ensures advantageous energy-storing and thus elastic deformation of the clamping section 109. This is furthermore improved if one or more slots 162 a, 162 b, 162 c are made in the further section 107 which have at least in sections an extension in the axial direction, in this embodiment three slots 162 a, 162 b, 162 c in the axial direction uniformly distributed in the circumferential direction; the slots 162 a, 162 b, 162 c can also extend obliquely to the axial direction. Except for the slots 162 a, 162 b, 162 c the shrink-fit tool holder 101 is rotationally symmetrical relative to its longitudinal axis.

The wall thickness which is provided in the further section 107 is especially dependent on the materials, the tool dimensions, and the workpiece to be machined. Due to the reduced wall thickness small differences of the cone angle can also be compensated by elastic deformation of the shrink-fit tool holder 101 and a higher true running accuracy of the overall system is achieved.

FIG. 12 shows a second embodiment of a shrink-fit tool holder 201 as claimed in the invention in a longitudinal section and FIG. 13 shows the pertinent perspective view. In the second embodiment the holding section 205 is offset from the middle to the end which holds the tool and is overlapped only to a lesser degree by the clamping area 263 which comprises the clamping section 209, the groove 210, and the conical section 212. On the end which holds the tool the holding section 205 can have a centering section as in the first embodiment. Moreover this end has a radius 261 of for example 0.1 to 5 mm, especially 0.2 to 3 mm, and preferably 0.4 to 2 mm, for simplified insertion of the tool. The overlap of the holding section 205 with the clamping area 263 is for example up to twice the clamping diameter.

On its end facing the clamping section 209 the shrink-fit tool holder 201 has an opening which forms the section 207 and which is part of the through hole. From the end, slots 262 a, 262 c are configured axially analogously to the second embodiment. A section of the opening which is set back from the end has an internal thread 264, into which a stop for the tool to be inserted can be precisely positioned. The axial extension of the further section 207 is for example twice the magnitude of the diameter of the further section 207. A transition section between the inside thread 264 and the holding section 203 is preferably free of threads.

Especially under unfavorable spatial conditions in the working space between the workpiece clamping area and the cutting tool this embodiment offers advantages especially for small milling tools, also because the elastically deformable region of the clamping area 263 is larger.

FIG. 14 shows a second embodiment of an adapter as claimed in the invention with the inserted shrink-fit tool holder, in a longitudinal section. The second embodiment has a base body 135 and an adapter insert 120. The adapter insert 120 can be assembled from two parts 120 a, 120 b, the interface running at a right angle to the plane of the drawings of FIG. 14 and parallel to the longitudinal axis of the configuration; preferably they are identical parts 120 a, 120 b. The adapter insert 120 consists of an electrically insulating material, preferably of a fiber-reinforced ceramic, especially of a ceramic reinforced with glass fibers.

The two parts 120 a, 120 b can be clamped to one another by means of a preferably closed ring 165. The ring 165 can be made of metal or also of a temperature-resistant plastic. The base body 135 on its end facing the adapter insert 120 has a connecting piece with a groove 138 formed on its inside into which the ring 165 can fit.

An adjustment pin which extends through the adapter insert 120 can be inserted or preferably screwed into the base body, preferably centrally, by which the axial position of the tool which can be inserted into the shrink-fit tool holder 1 can be adjusted with precision.

The depression 122 which faces the shrink-fit tool holder 1 and holds it extends in the axial direction so far that the clamping section 9 of the shrink-fit tool holder 1 is essentially overlapped. In this way the clamping section 9 is covered during heating and a change of the surface for example by oxidation is thus advantageously prevented. To this end, the conical shape of the depression 122 can be matched to the conical shape of the shrink-fit tool holder 1 such that air is essentially excluded. Moreover the shrink-fit tool holder 1 is reliably fixed in the adapter insert 120. Furthermore the shrink-fit tool holder 1 can be easily removed after shrink-fitting by the multipart adapter insert 120. With inductive heating in the electrically insulating adapter insert 120 no current is induced and heat forms in spite of the overlapping of the adapter insert 120 in the shrink-fit tool holder 1. 

1. Tool retraction receiving element with a receiving section (3) for retracting a tool (15) and a clamping section (9) for clamping the tool retraction receiving element (1) in a tool receiving carrier, characterized in that the receiving section (3) for the tool (15) and the clamping section (9) of the tool retraction receiving element (1) overlap in the longitudinal direction.
 2. The shrink-fit tool holder as claimed in claim 1, wherein the overlapping is more than 30% of the total length of the shrink-fit tool holder (1), especially more than 50%.
 3. The shrink-fit tool holder as claimed in claim 2, wherein the overlapping extends essentially over the entire length of the clamping section (9) for clamping the shrink-fit tool holder (1) in a tool holder support.
 4. The shrink-fit tool holder as claimed in claim 1, wherein the holding section (3) for shrink fitting of the tool is formed by a through hole which extends over the entire length of the shrink-fit tool holder.
 5. The shrink-fit tool holder as claimed in claim 4, wherein the through hole (3) on its end opposite the clamping section (9) has a centering section (6) with a widened inside diameter.
 6. The shrink-fit tool holder as claimed in claim 1, wherein following the clamping section (9) a circumferential groove (10) is formed which has an especially rectangular cross section.
 7. The shrink-fit tool holder as claimed in claim 6, wherein on the end of the shrink-fit tool holder (1) opposite the clamping section (9), following the circumferential groove (10) a conical section (12) is formed which widens toward the circumferential groove (10).
 8. The shrink-fit tool holder as claimed in claim 1, wherein the clamping section (9) has the shape of a cone.
 9. The shrink-fit tool holder as claimed in claim 1, wherein the clamping section has the shape of a circular cylinder.
 10. The shrink-fit tool holder as claimed in claim 1, wherein the holding section (103) is formed by an opening which extends in the longitudinal direction of the shrink-fit tool holder (101), preferably by a through hole which extends over the entire length, and that the end of the opening which holds the tool is radially widened, especially has a radius (161).
 11. The shrink-fit tool holder as claimed in claim 1, wherein on its end facing the clamping section (109) the shrink-fit tool holder (101) has an opening which extends in the longitudinal direction of the shrink-fit tool holder (101) and which forms a further section (107), with a diameter which is greater than the diameter of the holding section (103).
 12. The shrink-fit tool holder as claimed in claim 11, wherein the further section (107) has slots (162 a, 162 b, 162 c) with an axial extension.
 13. The shrink-fit tool holder as claimed in claim 11, wherein the further section (207) has an inside thread (264).
 14. Adapter for positioning a shrink-fit tool holder (1) as claimed in claim 1, characterized by a depression (22) with dimensions which are matched to the end of the clamping section (9) of the shrink-fit tool holder (1).
 15. The adapter as claimed in claim 14, wherein the adapter (20) tapers toward the shrink-fit tool holder (1).
 16. The adapter as claimed in claim 14, wherein the adapter is configured as at least two parts and comprises a base adapter (35) and an adapter insert (20) on which the depression (22) and/or the tapering (29, 31) is/are configured.
 17. The adapter as claimed in claim 16, wherein the adapter insert (120) is two-part, especially can be assembled from two identical parts (120 a, 120 b).
 18. The adapter as claimed in claim 14, characterized by a central threaded hole (41) in which a threaded bolt (50) is held with a turning capacity, with a free end which forms a stop for the tool when the shrink-fit tool holder (1) is positioned on the adapter (20).
 19. The adapter as claimed in claim 14, wherein the depression (122) extends in the axial direction so far that the clamping section (9) of the shrink-fit tool holder (1) is essentially overlapped.
 20. The adapter as claimed in claim 14, wherein the adapter at least in sections consists of an electrically insulating material, especially of a ceramic material. 